Orbital box diagrams visualize how electrons fill atomic orbitals using up and down arrows. Each box represents one orbital; paired electrons (both spins) fill a box fully. Unpaired electrons sit alone in their box. This tool applies the Aufbau principle, Hund's rule, and Pauli exclusion principle to generate accurate orbital diagrams for any element.
How to Read Orbital Box Diagrams
Orbital box diagrams provide a visual representation of electron spin in each orbital. They are especially useful for understanding magnetic properties, bond formation, and excited state transitions. Each box represents one orbital; arrows represent electrons with their spin orientation.
Example: Nitrogen (N, Z=7)
Nitrogen has 7 electrons. The filling order is: 1s gets 2 electrons (filled), 2s gets 2 electrons (filled), and 2p gets 3 electrons. For the 2p subshell with 3 orbitals and 3 electrons, Hund's rule says to place one electron in each 2p orbital before doubling up. Result: each 2p orbital has exactly one spin-up electron. Nitrogen has 3 unpaired electrons, making it paramagnetic. The diagram shows: 1s[↑↓] 2s[↑↓] 2p[↑][↑][↑].
The Three Quantum Mechanics Rules
Aufbau Principle: Electrons fill the lowest-energy orbitals first. The energy order is not simply 1s, 2s, 2p, 3s... — at higher energies, the 4s orbital is filled before 3d, and 6s before 4f. This is why Potassium (K, Z=19) has its 19th electron in 4s, not 3d.
Hund's Rule: In a degenerate subshell (p has 3 equal-energy orbitals, d has 5, f has 7), electrons spread out before doubling up. All singly-occupied orbitals have the same spin orientation. This minimizes electron-electron repulsion by maximizing the spatial separation of electrons.
Pauli Exclusion Principle: No two electrons in an atom can have the same four quantum numbers (n, l, m_l, m_s). Practically, each orbital holds at most 2 electrons with opposite spins (↑↓). This is why each box can hold at most one pair of arrows.
Transition Metal Diagrams
Transition metals show d orbital filling from 4s to 3d. For example, Manganese (Mn, Z=25) has [Ar] 3d⁵ 4s² — the five 3d orbitals each contain one spin-up electron (half-filled), plus both 4s electrons paired. This is a particularly stable configuration. Iron (Fe, Z=26) adds one more electron to pair in one 3d orbital, giving 4 unpaired electrons and strong paramagnetism.
FAQ
What is an orbital box diagram?
An orbital box diagram (or orbital filling diagram) shows electrons as up and down arrows inside boxes, where each box represents one atomic orbital. The diagram visually shows how electrons fill orbitals following Aufbau order, Hund's rule (fill each orbital singly before pairing), and the Pauli exclusion principle (max 2 electrons per orbital with opposite spins).
What is Hund's rule?
Hund's rule states that electrons occupy orbitals in the same subshell singly before any orbital is doubly occupied, and all singly-occupied orbitals have the same spin (all spin-up before spin-down). For example, in Carbon (C) with 2p² electrons, the two p electrons each occupy separate 2p orbitals with parallel spins rather than pairing in one orbital.
What is the Aufbau principle?
The Aufbau principle (from German 'building up') states that electrons fill atomic orbitals starting with the lowest energy orbital: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. This produces the most stable ground state electron configuration.
What is the Pauli exclusion principle?
The Pauli exclusion principle states that no two electrons in an atom can have the same four quantum numbers. Practically, this means each orbital can hold at most 2 electrons, and they must have opposite spins (one spin-up ↑ and one spin-down ↓).
How do I count unpaired electrons?
Count the boxes with only one arrow (one electron). Unpaired electrons determine paramagnetic properties. Nitrogen (N) has 3 unpaired electrons in its 2p subshell. A completely filled or empty subshell has 0 unpaired electrons. Transition metals often have many unpaired d electrons — Iron (Fe) has 4.
What does paramagnetic mean?
Paramagnetic atoms have unpaired electrons and are weakly attracted to external magnetic fields. The more unpaired electrons, the stronger the paramagnetic effect. Diamagnetic atoms have all electrons paired and are weakly repelled. Iron, cobalt, and nickel are examples of strongly magnetic elements due to many unpaired 3d electrons.
Is this orbital diagram tool free?
Yes, completely free. No account or signup needed. All calculations and diagram rendering run in your browser.